Basically, Since i'm using a keyboard to play Pokemon XD, It doesn't give me the feature to walk slowly, and in this case, you need to walk slowly in order to advance the story in this one part. Just a simple problem, but if i don't find a way to start walking slowly, then i won't be able to continue the game...Please help me! (P.S. I'm on mac os x.)

Yo, click on the GCPad button in Dolphin to configure your controller. Where it says Main Stick, you need to set a button for Modifier. This (I assume) allows you to set how much/far the Main Stick in tilted in any direction. Press the button you assigned to Modifier to change this. Haven't tried it myself, but here's an image of what you should be looking at: